Tactical shoulder rifles enable rapid high-volume fire that can heat the rifle barrel to very high temperatures. To protect the rifleman against contact with the hot surface, and to help dissipate the heat, the barrel is usually shrouded by a handguard or grip that completely encloses the portion of the barrel directly in front of the receiver over a length sufficient to provide a grip area for the rifleman's lead hand. This type of forearm handguard is usually “free-floating”, i.e. connected to the rifle only at end-cap fittings and not directly in contact with the barrel. The handguard thus creates an air space around the barrel to retard heat conduction from the barrel into the handguard. The handguard is vented with air holes or slots to allow heat convection out of the enclosed air space. An early example of this type handguard is described in U.S. Pat. No. 2,965,994. The handguard described in this reference has a laminated construction, comprising a fiberglass-reinforced plastic outer skin laminated to a low-density foam core, with the inner surface covered by a reflecting foil.
Forearm handguards can have a generally triangular or pear-like sectional shape wherein the base is wider and more flat than the top, as in the earlier versions of M16. This configuration provides a wider support area for the palm when firing offhand, and a more stable platform when firing over a rest, than would a handguard with a narrow bottom. However, there are advantages to a generally cylindrical handguard wherein the top and bottom pieces are identical mating semi-oval half-pieces, such as described in U.S. Pat. Nos. 4,536,982 and 4,663,875. In such handguards, the area at the center of the half pieces (top and bottom of the assembled handguard) is a flat longitudinal rib with a row of vent holes. The exterior of the top and bottom half-pieces described in U.S. Pat. No. 4,536,982 have laterally extending ribs over most of the surface to enhance structural integrity and provide a firm grip, while the flat longitudinal rib has small longitudinal grooves, perhaps to improve the rest characteristic.
It is also known to attach one or more rail adapters to or along a forearm handguard to mount various accessories to the rifle, as described in U.S. Pat. Nos. 5,826,363; 5,590,484 and 5,198,600. When an adapter rail is not being used, it can be protected by covering it with a panel that slides along the grooves at the sides of the rail, as shown in the above U.S. Pat. No. 5,826,363.
Recent improvements in handguard technology are disclosed in commonly owned U.S. Pat. No. 6,609,321. The handguard is lightweight and easily assembled, combining several features shown in the above references, with improvements in how the features are interrelated. In particular, the handguard is made of two injection-molded plastic half-grip pieces, at least one of which has an integrally-molded accessory rail that it is recessed in the area at the center of the half-grip piece. This recessed positioning locates the ribs and guide channel of the rail inside what would be the extended arc of the sides of the half-grip piece in the traditional handguard of this type. A rail cover is provided that replicates the extended arc of the sides of the half-grip piece up to a flat longitudinally extending rib along the center of the cover. Thus, with the cover installed, the grip has essentially the same feel and dimensions as the traditional oval grip as described and shown in U.S. Pat. Nos. 4,536,982 and 4,663,875. Vent holes may be positioned between the opposing ribs of the rail, and the cover may have matching vent holes in registry with the holes between the rails.